1. Field of the Invention
The present invention relates to a heavy duty tire which can reduce deformation of the bead portion caused by the increase in usable years.
2. Description of the Prior Art
In FIG. 11, there is shown a structure of a bead portion of a conventional heavy duty tire. The bead portion comprises a carcass ply “a” including a main portion a1 and a pair of turnup portions a2 each wound around a bead core b.
In such a structure, since an outer end a2e of the turnup portion “a2” is positioned near a radially outer surface of the bead core b, a stress applied to the end a2e of the turnup portion at a time when the bead portion is deformed is small. Accordingly, it is possible to prevent some damages such as a loose from the end a2e or the like.
However, in such a bead structure, a large moment M around the center b1 of the cross section of the bead core b tends to be generated by tension F of the carcass cords. The moment M applied into the bead core b makes the bead portion deform such that a toe “c” thereof is lifted from a rim seat (not shown).
The deformation of the bead portion becomes large by the increase of usable years and generates a gap between the toe “c” of the bead portion and the rim with this, when an used tire (including a re-tread tire) is remounted on the rim, it is hard to inflate the tire, since the air to be filled in the tire tends to leak through the gap.